The primary hypotheses to be tested are (1) many adult and pediatric onset oxidative phosphorylation (OXPHOS) diseases are caused by mutations in the mitochondrial DNA (mtDNA); (2) impairment of OXPHOS produces compensatory changes in both nuclear and mitochondrial OXPHOS gene expression; (3) cellular acidosis produces increased expression of genes for protein degradation; and (4) the clinical symptoms may respond to coenzyme Q10, a drug that may enhance OXPHOS electron transport. This project is part of a large NIH project, and will be ongoing over the next 4 years. A comprehensive control group of approximately 60 participants, ranging in age from 20-80 yrs, has been established.